Particle based electrodes and methods of making same

ABSTRACT

A coated electrode is provided for use in energy storage devices. The coated electrode comprises a dry fibrillized polymer that is fibrillized with no processing additives.

RELATED APPLICATIONS

The present invention is related to and claims priority from commonlyassigned Provisional Application No. 60/486,002, filed Jul. 9, 2003,which is incorporated herein by reference; and

the present invention is related to and claims priority from commonlyassigned Provisional Application No. 60/498,346, filed Aug. 26, 2003,which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of coating ofstructures for use in energy storage devices. More particularly, thepresent invention relates to capacitor structures and methods that usedry fibrillized flouropolymers.

BACKGROUND INFORMATION

Double-layer capacitors, also referred to as ultracapacitors andsuper-capacitors, are energy storage devices that are able to store moreenergy per unit weight and unit volume than capacitors made withtraditional technology.

Double-layer capacitors store electrostatic energy in a polarizedelectrode/electrolyte interface layer. Double-layer capacitors includetwo electrodes, which are separated from contact by a porous separator.The separator prevents an electronic (as opposed to an ionic) currentfrom shorting the two electrodes. Both the electrodes and the porousseparator are immersed in an electrolyte, which allows flow of the ioniccurrent between the electrodes and through the separator. At theelectrode/electrolyte interface, a first layer of solvent dipole and asecond layer of charged species is formed (hence, the name“double-layer” capacitor).

Although, double-layer capacitors can theoretically be operated atvoltages as high as 4.0 volts and possibly higher, current double-layercapacitor manufacturing technologies limit nominal operating voltages ofdouble-layer capacitors to about 2.5 to 2.7 volts. Higher operatingvoltages are possible, but at such voltages undesirable destructivebreakdown begins to occur, which in part may be due to interactions withimpurities and residues that can be introduced during manufacture. Forexample, undesirable destructive breakdown of double-layer capacitors isseen to appear at voltages between about 2.7 to 3.0 volts. Double-layercapacitor can also provide high capacitance on the order of 1 to 5000Farads in relatively small form factor housings.

Known capacitor electrode fabrication techniques utilize coating andextrusion processes. Both processes utilize binders such as polymers orresins to provide cohesion between the surface areas of the particlesused.

In the coating process, the binder is dissolved in an appropriatesolvent, typically organic, aqueous or blends of aqueous and organics,and mixed with the conductive material, such as carbon, to form aslurry. The slurry is then coated through a doctor blade or a slot dieonto the current collector, and the resulting electrode is dried toremove the solvent. Among the numerous polymers and copolymers that canbe used as a binder in the coating process, most of them suffer from alack of stability when a subsequent electrolyte solvent is used toimpregnate a final capacitor product. This is especially true when thesolvent is an organic one and the working or storage temperature ishigher than 65° C. Instability of the binder can lead to a prematurefailure of an electrode and, thus a capacitor.

Typical extrusion processes use the fibrillation properties of certainpolymers to provide a matrix for embedded conductive material. Some ofthe polymers in the family of flouropolymers, such aspolytetrafluoroethylene (PTFE), are particularly inert and stable in thecommon electrolyte solvents used in double-layer capacitors, even thoseusing organic solvent at high working or storage temperatures. Thus, thestability of an electrode made using PTFE can be higher than those madewith other binders. Polymers and similar ultra-high molecular weightsubstances capable of fibrillization are also commonly referred to as“fibrillizable binders” or “fibril-forming binders.” Fibril-formingbinders find use with powder like materials. In one prior art process,fibrillizable binder and powder materials are mixed with solvent,lubricant, or the like, and the resulting wet mixture is subjected tohigh-shear forces to sufficiently fibrillize the binder particles.Fibrillization of the binder particles produces fibrils that eventuallyform a matrix or lattice for supporting the resulting composition ofmatter. The resulting dough-like material is calendared many times toproduce a conductive film of desired thickness and density. In the priorart, the high shear forces can be provided by subjecting the mixture toan extruder.

In the prior art, the resulting additive based extruded product issubsequently processed in a high-pressure compactor, dried to remove theadditive, shaped into a needed form, and otherwise processed to obtainan end-product for the needed application. For purposes of handling,processing, and durability, desirable properties of the end producttypically depend on the consistency and homogeneity of the compositionof matter from which the product is made, with good consistency andhomogeneity being important requirements. Such desirable propertiesdepend on the degree of fibrillization of the polymer. Tensile strengthcommonly depends on both the degree of fibrillization of thefibrillizable binder, and the consistency of the fibril lattice formedby the binder within the material. When used as an electrode, internalresistance of an electrode film is also important.

Internal resistance may depend on bulk resistivity—volume resistivity onlarge scale—of the material from which an electrode film is fabricated.Bulk resistivity of the material is a function of the material'shomogeneity; the better the dispersal of the conductive carbon particlesor other conductive filler within the material, the lower theresistivity of the material. When electrode films are used incapacitors, such as double-layer capacitors, capacitance per unit volumeis yet another important characteristic. In double layer capacitors,capacitance increases with the specific surface area of the electrodefilm used to make a capacitor electrode. Specific surface area isdefined as the ratio of (1) the surface area of electrode film exposedto an electrolytic solution when the electrode material is immersed inthe solution, and (2) the volume of the electrode film. An electrodefilm's specific surface area and capacitance per unit volume arebelieved to improve with improvement in consistency and homogeneity.

Because fluoropolymers do not dissolve in most solvents, they are notsuited for use as a binder in conventional solvent based coatingprocesses. Because extrusion processes require large manufacturingequipment investments, it is often financially prohibitive for electrodemanufacturers to adopt manufacturing processes that take advantage ofthe benefits of using fluoropolymers as a binder. As such, it would bedesirable to use fluoropolymers in the manufacture of coated electrodes.

SUMMARY

In accordance with embodiments of the present invention, fibrillizablepolymers and methods of using in manufacture of energy storage devicesare described. The present invention provides methods for making longlasting, durable, and inexpensive energy storage devices, for example,capacitors. Fibrillization of the polymers is provided without the useof any processing additives. The present invention provides distinctadvantages when compared to that of the coating based methods of theprior art. A high throughput method for making more durable and morereliable coating based energy storage devices is provided.

In one embodiment, a method of making a slurry coated electrodecomprises the steps of dry blending dry carbon particles and dry binderto form a mixture that comprises the carbon particles and the drybinder; liquefying the mixture with a solution to form a slurry;applying the slurry to a current collector; drying the slurry; andcompacting the current collector and slurry. The step of blending maycomprise a step of dry fibrillizing the mixture. The dry fibrillizingstep may comprise milling the mixture. The dry fibrillizing step maycomprise subjecting the mixture to high shear forces. The dryfibrillizing step may utilize a high-pressure gas. The high-pressure gasmay comprise a pressure of more than 60 PSI. The gas may comprise a dewpoint of no more than −40 degrees F., water content 12PPM. The methodmay comprise a step of treating the current collector prior to applyingthe slurry to improve adhesion between the current collector and slurry.The step of treating the current collector may comprise coating thecurrent collector with a bonding agent prior to applying the slurry. Thestep of treating the current collector may comprise roughening a surfaceof the current collector prior to applying the slurry. The dry bindermay comprise fluoropolymer particles. The fluoropolymer particles maycomprise PTFE. The mixture may comprise conductive particles. Themixture may comprise activated carbon particles. The mixture maycomprise approximately 50% to 99% activated carbon. The mixture maycomprise approximately 0% to 25% conductive carbon. The mixture maycomprise approximately 0.5% to 20% fluoropolymer particles. The mixturemay comprise approximately 80% to 95% activated carbon, approximately 0%to 15% conductive carbon, and approximately 3% to 15% fluoropolymer. Thesolution may comprise deionized water. The current collector maycomprise aluminum. The step of applying the suspension further maycomprise coating the current collector with the slurry using a doctorblade, a slot die, or a direct or reverse gravure process.

In one embodiment, a blend of dry particles fibrillized for use in themanufacture of a coated electrode comprises a mixture of dry fibrillizeddry carbon and dry binder particles. The binder particles may comprise apolymer, and wherein the carbon particles comprise activated andconductive carbon. The binder may comprise fluoropolymer particles. Thebinder may comprise PTFE. The binder may comprise particles subject tohigh shear forces. The high shear forces may be applied by gas at morethan about 60 PSI. The binder may comprise milled polymer particles. Thebinder may comprise jet milled polymer particles. The binder maycomprise hammer milled polymer particles. The electrode may be an energystorage device electrode. The energy storage device may be a capacitor.

In one embodiment, an electrode comprises a dry blend of dry binder anddry carbon particles subjected to high shear forces. The blend maycomprise approximately 50% to 99% activated carbon. The blend maycomprise approximately 0% to 25% conductive carbon. The blend maycomprise approximately 0.5% to 20% fluoropolymer. The blend may compriseapproximately 80% to 95% activated carbon, approximately 0% to 15%conductive carbon, and approximately 3% to 15% fluoropolymer. Theelectrode may be a capacitor electrode. The electrode may be adouble-layer capacitor electrode. The electrode may be a batteryelectrode. The electrode may be a fuel-cell electrode. The electrode maycomprise a current collector, wherein the binder and conductiveparticles are formed as a slurry coupled to the current collector.

In one embodiment, a capacitor product comprises a dry fibrillized blendof particles subjected to high shear forces, the particles includingbinder and carbon particles; and one or more current collector, whereinthe blend of dry particles are coated onto the one or more currentcollector. The one or more current collector and the dry particles maybe disposed a bonding layer. The one or more current collector maycomprise aluminum. The product may comprise a housing, wherein the oneor more current collector is shaped as a roll, wherein the roll isdisposed within the housing. Within the housing may be disposed anelectrolyte. The electrolyte may comprise acetonitrile. The capacitormay be rated to operate at a voltage of no more than about 3.0 volts. Inone embodiment, an energy storage device comprises dry fibrillizedelectrode means for providing coated functionality in a coated energystorage device.

In one embodiment, a capacitor, the capacitor comprises a housing; acover; a collector, the collector disposed in the housing, the collectorcomprising two ends, a first end coupled to the housing, a second endcoupled to the cover; a dried electrode slurry, the dried electrodeslurry disposed as a coating onto the collector, the dried electrodeslurry comprising a dry fibrillized blend of dry carbon and dry polymer,the dry fibrillized blend of dry carbon and dry polymer formed as a drymixture comprised of essentially or substantially no processingadditive; and an electrolyte, the electrolyte disposed in the housing.The capacitor may comprise a capacitance of greater than 1 Farad.

Other embodiments, benefits, and advantages will become apparent upon afurther reading of the following Figures, Description, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a block diagram illustrating a method for making an energystorage device electrode.

FIG. 1 b is a high-level front view of a jet mill assembly used tofibrillize binder within a dry carbon particle mixture.

FIG. 1 c is a high-level side view of a jet mill assembly shown in FIG.1 b;

FIG. 1 d is a top view of the jet mill assembly shown in FIGS. 1 b and 1c.

FIG. 1 e is a high-level front view of a compressor and a compressed airstorage tank used to supply compressed air to a jet mill assembly.

FIG. 1 f is a high-level top view of the compressor and the compressedair storage tank shown in FIG. 1 e, in accordance with the presentinvention.

FIG. 1 g is a high-level front view of the jet mill assembly of FIGS. 1b-d in combination with a dust collector and a collection container.

FIG. 1 h is a high-level top view of the combination of FIGS. 1 f and 1g.

FIGS. 1 i, 1 j, and 1 k illustrate effects of variations in feed rate,grind pressure, and feed pressure on tensile strength in length, tensilestrength in width, and dry resistivity of electrode materials.

FIG. 1 m illustrates effects of variations in feed rate, grind pressure,and feed pressure.

FIG. 1 n illustrates effects of variations in feed rate, grind pressure,and feed pressure on capacitance.

FIG. 1 p illustrates effect of variation in feed pressure on internalresistance of electrodes, and on the capacitance of double layercapacitors using such electrodes.

FIG. 2 shows an apparatus for forming a coated electrode.

FIG. 3 is a representation of a rolled electrode coupled internally to ahousing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to several embodiments of theinvention that are illustrated in the accompanying drawings. Inaccordance with embodiments of the present invention, fibrillizablepolymers and methods of using in manufacture of energy storage devicesare described. The present invention provides methods for making longlasting, durable, and inexpensive energy storage devices, for example,capacitors. Fibrillization of the polymers is provided without the useof any processing additives. The present invention provides distinctadvantages when compared to that of the coating based methods of theprior art. A high throughput method for making more durable and morereliable coating based energy storage devices is provided.

In the embodiments that follow, it will be understood that reference tono-use and non-use of additive(s) in the manufacture of an energystorage device according to the present invention takes into accountthat electrolyte may be used during a final electrode electrolyteimmersion/impregnation step. An electrode electrolyteimmersion/impregnation step is typically utilized prior to providing afinal finished capacitor electrode in a sealed housing. Furthermore,even though additives, such as solvents, liquids, and the like, are notused in the dry fibrillization of polymers and dry particles inembodiments disclosed herein, during fibrillization, a certain amount ofimpurity, for example, moisture, may be absorbed or attach itself from asurrounding environment. Those skilled in the art will understand thatthe dry particles used with embodiments and processes disclosed hereinmay also, prior to their being provided by particle manufacturers as dryparticles, have themselves been pre-processed with additives, liquids,solvents, etc., and, thus, comprise one or more pre-process residuethereof. It is identified that even after one or more drying step, traceamounts of the aforementioned pre-process residues and impurities may bepresent in the dry fibrillization process steps described herein.

Referring now to FIG. 1 a, a block diagram illustrating a process formaking an energy device using dry fibrillized binder is shown. Theprocess shown in FIG. 1 a begins by dry blending dry carbon particlesand dry binder particles together. Those skilled in the art willunderstand that depending on particle size, particles can be describedas powders and the like, and that reference to particles is not meant tobe limiting to the embodiments described herein, which should be limitedonly by the appended claims and their equivalents. For example, withinthe scope of the term “particles,” the present invention contemplatespowders, spheres, platelets, flakes, fibers, nano-tubes, and otherparticles with other dimensions and other aspect ratios. In oneembodiment, dry carbon particles as referenced herein refers toactivated carbon particles 12 and/or conductive particles 14, and binderparticles 16 as referenced herein refers to an inert dry binder. In oneembodiment, conductive particles 14 comprise conductive carbonparticles. In one embodiment, conductive particles 14, may comprisegraphite. In one embodiment, it is envisioned that conductive particles14 may comprise a metal powder or the like. In one embodiment, drybinder 16 comprises a fibrillizable polymer, for example,polytetrafluoroethylene (PTFE) particles. Other fibrillizable bindersenvisioned for use herein include ultra-high molecular weightpolypropylene, polyethylene, co-polymers, polymer blends and the like.It is understood that the present invention should not be limited by thedisclosed or suggested binder, but rather, by the claims that follow. Inone embodiment, particular mixtures of particles 12, 14, and binder 16comprise about 50% to 99% activated carbon, about 0% to 25% conductivecarbon, and/or about 0.5% to 50% binder by weight. In a more particularembodiment, particle mixtures include about 80% to 90% activated carbon,about 0% to 15% conductive carbon, and about 3% to 15% binder by weight.In one embodiment, the activated carbon particles 12 comprise a meandiameter of about 10 microns. In one embodiment, the conductive carbonparticles 14 comprise a range of diameters of less than 20 microns. Inone embodiment, the binder particles 16 comprise a mean diameter ofabout 450 microns. Suitable carbon powders are available from a varietyof sources, including YP-17 activated carbon particles sold by KurarayChemical Co., LTD, Shin-hankyu Bldg. 9F Blvd. C-237, 1-12-39 Umeda,Kiata-ku, Osaka 530-8611, Japan; and BP 2000 conductive particles soldby Cabot Corp. 157 Concord Road, P.O. Box 7001, Billerica, Mass.01821-7001, Phone: 978 663-3455.

In step 18, particles of activated carbon, conductive carbon, and binderprovided during respective steps 12, 14, and 16 are dry blended togetherto form a dry mixture. In one embodiment, dry particles 12, 14, and 16are blended for 1 to 10 minutes in a V-blender equipped with a highintensity mixing bar until a uniform dry mixture is formed. Thoseskilled in the art will identify that blending time can vary based onbatch size, materials, particle size, densities, as well as otherproperties, and yet remain within the scope of the present invention.With reference to blending step 18, in one embodiment, particle sizereduction and classification can be carried out as part of the blendingstep 18, or prior to the blending step 18. Size reduction andclassification may improve consistency and repeatability of theresulting blended mixture and, consequently, of the quality of electrodefilms and electrodes fabricated therefrom.

After dry blending step 18, dry binder 16 within the dry particles isfibrillized in a dry fibrillizing step 20. The dry fibrillizing step 20is effectuated using a dry solventless and liquidless high sheartechnique. During dry fibrillizing step 20, high shear forces areapplied to dry binder 16 in order to physically stretch it. Thestretched binder forms a network of thin web-like fibers that act toenmesh, entrap, bind, and/or support the dry particles 12 and 14. In oneembodiment, fibrillizing step 20 may be effectuated using a jet mill.Referring to now to FIGS. 1 b, 1 c, and 1 d, there is seen,respectively, front, side, and top views of a jet mill assembly 100 usedto perform a dry fibrillization step 20. For convenience, the jet millassembly 100 is installed on a movable auxiliary equipment table 105,and includes indicators 110 for displaying various temperatures and gaspressures that arise during operation. A gas input connector 115receives compressed air from an external supply and routes thecompressed air through internal tubing (not shown) to a feed air hose120 and a grind air hose 125, which both lead and are connected to a jetmill 130. The jet mill 130 includes: (1) a funnel-like materialreceptacle device 135 that receives compressed feed air from the feedair hose 120, and the blended carbon-binder mixture of step 18 from afeeder 140; (2) an internal grinding chamber where the carbon-bindermixture material is processed; and (3) an output connection 145 forremoving the processed material. In the illustrated embodiment, the jetmill 130 is a 4-inch Micronizer® model available from Sturtevant, Inc.,348 Circuit Street, Hanover, Mass. 02339; telephone number (781)829-6501. The feeder 140 is an AccuRate® feeder with a digital dialindicator model 302M, available from Schenck AccuRate®, 746 E. MilwaukeeStreet, P.O. Box 208, Whitewater, Wis. 53190; telephone number (888)742-1249. The feeder includes the following components: a 0.33 cubic ft.internal hopper; an external paddle agitation flow aid; a 1.0-inch, fullpitch, open flight feed screw; a % hp, 90VDC, 1,800 rpm, TENV electricmotor drive; an internal mount controller with a variable speed, 50:1turndown ratio; and a 110 Volt, single-phase, 60 Hz power supply with apower cord. The feeder 140 dispenses the carbon-binder mixture providedby step 18 at a preset rate. The rate is set using the digital dial,which is capable of settings between 0 and 999, linearly controlling thefeeder operation. The highest setting of the feeder dial corresponds toa jet mill output of about 12 kg per hour.

The feeder 140 appears in FIGS. 1 b and 1 d, but has been omitted fromFIG. 1 c, to prevent obstruction of view of other components of the jetmill 130. The compressed air used in the jet mill assembly 100 isprovided by a combination 200 of a compressor 205 and a compressed airstorage tank 210, illustrated in FIGS. 1 e and 1 f; FIG. 1 e is a frontview and FIG. 1 f is a top view of the combination 200. The compressor205 used in this embodiment is a GA 30-55C model available from AtlasCopco Compressors, Inc., 161 Lower Westfield Road, Holyoke, MA 01040;telephone number (413) 536-0600. The compressor 205 includes thefollowing features and components: air supply capacity of 180 standardcubic feet per minute (“SCFM”) at 125 PSIG; a 40-hp, 3-phase, 60 HZ, 460VAC premium efficiency motor; a WYE-delta reduced voltage starter;rubber isolation pads; a refrigerated air dryer; air filters and acondensate separator; an air cooler with an outlet 206; and an aircontrol and monitoring panel 207. The 180-SCFM capacity of thecompressor 205 is more than sufficient to supply the 4-inch Micronizer®jet mill 130, which is rated at 55 SCFM. The compressed air storage tank210 is a 400-gallon receiver tank with a safety valve, an automaticdrain valve, and a pressure gauge. The compressor 205 providescompressed air to the tank 205 through a compressed air outlet valve206, a hose 215, and a tank inlet valve 211.

It is identified that the compressed air provided under high-pressure bycompressor 205 is preferably as dry as possible. In one embodiment, arange of acceptable dew point for the air is about −20 to −40 degreesF., and water content of less than about 20 ppm. Although discussed asbeing effectuated by high-pressure air, it is understood that othersufficiently dry gases are envisioned as being used to fibrillize binderparticles utilized in embodiments of the present invention, for example,oxygen, nitrogen, helium, and the like. In one embodiment, the gas maycomprise a dew point between about −20 and −40 degrees F., and a watercontent of less than about 20 PPM.

In the jet mill 130, the carbon-binder mixture is inspired by venturiand transferred by the compressed feed air into a grinding chamber,where the fibrillization of the mixture takes place. The grindingchamber, which has a generally cylindrical shape, includes one or morenozzles placed circumferentially. The nozzles discharge the compressedgrind air that is supplied by the grind air hose 125. The compressed airjets injected by the nozzles accelerate the carbon-binder particles andcause predominantly particle-to-particle collisions, although someparticle-wall collisions also take place. The collisions dissipate theenergy of the compressed air relatively quickly, fibrillizing the drybinder 16 within the mixture and embedding carbon particle 12 and 14aggregates and agglomerates into the lattice formed by the fibrillizedbinder. The collisions may also cause size reduction of the carbonaggregates and agglomerates. The colliding particles 12, 14, and 16spiral towards the center of the grinding chamber and exit the chamberthrough the output connection 145.

Referring now to FIGS. 1 g and 1 h, there are seen front and top views,respectively, of the jet mill assembly 100, a dust collector 160, and acollection container 170. In one embodiment, the fibrillizedcarbon-binder particles that exit through the output connection 145 areguided by a discharge hose 175 from the jet mill 130 into a dustcollector 160. In the illustrated embodiment, the dust collector 160 ismodel CL-7-36-11 available from Ultra Industries, Inc., 1908 DeKovenAvenue, Racine, Wis. 53403; telephone number (262) 633-5070. Within thedust collector 160 the output of the jet mill 130 is separated into (1)air and dust, and (2) a dry fibrillized carbon-binder particle mixture20. The carbon-binder mixture is collected in the container 170, whilethe air is filtered by one or more filters to remove the dust, and thendischarged. The filters, which may be internal or external to the dustcollector 160, are periodically cleaned, and the dust is discarded.Operation of the dust collector is directed from a control panel 180.

It has been identified that a dry compounded material, which is providedby dry fibrillization step 20, retains its homogeneous particle likeproperties for a limited period of time. In one embodiment, because offorces, for example, gravitational forces exerted on the dry particles12, 14, and 16, the compounded material begins to settle such thatspaces and voids that exist between the dry particles 12, 14, 16 afterstep 20 gradually become reduced in volume. In one embodiment, after arelatively short period of time, for example 10 minutes or so, the dryparticles 12, 14, 16 compact together and begin to form clumps or chunkssuch that the homogeneous properties of the compounded material may bediminished and/or such that downstream processes that require freeflowing compounded materials are made more difficult to achieve.

Accordingly, in one embodiment, it is identified that a dry compoundedmaterial as provided by step 20 should be utilized before itshomogeneous properties are no longer sufficiently present and/or thatsteps are taken to keep the compounded material sufficiently aerated toavoid clumping. It should be noted that the specific processingcomponents described so far may vary as long as the intent of theembodiments described herein is achieved. For example, techniques andmachinery that are envisioned for potential use to provide high shearforces to effectuate a dry fibrillization step 20 include jet milling,pin milling, impact pulverization, and hammer milling, and othertechniques and apparatus that can provide sufficiently high shear forcesto a dry material. Further in example, a wide selection of dustcollectors can be used in alternative embodiments, ranging from simplefree-hanging socks to complicated housing designs with cartridge filtersor pulse-cleaned bags. Similarly, other feeders can be easilysubstituted in the assembly 100, including conventional volumetricfeeders, loss-weight volumetric feeders, and vibratory feeders. Thesize, make, and other parameters of the jet mill 130 and the compressedair supply apparatus (the compressor 205 and the compressed air storagetank 210) may also vary and yet be within the scope of the presentinvention.

The present inventors have performed a number of experiments toinvestigate the effects of three factors in the operation of jet millassembly 100 on qualities of the dry compounded material provided by dryfibrillization step 20, and on compacted electrode films fabricatedtherefrom. The three factors are these: (1) feed air pressure, (2) grindair pressure, and (3) feed rate. The observed qualities included tensilestrength in width (i.e., in the direction transverse to the direction ofmovement of a electrode film in a high-pressure calender during acompacting process); tensile strength in length (i.e., in the directionof the film movement); resistivity of the dry jet mill processed mixtureprovided by dry fibrillization step 20; internal resistance of compactedelectrode films; and specific capacitance achieved in a double layercapacitor application. Resistance and specific capacitance values wereobtained for both charge (up) and discharge (down) capacitor cycles.

The design of experiments (“DOE”) included a three-factorial, eightexperiment investigation performed with electrode films dried for 3hours under vacuum conditions at 160 degrees Celsius. Five or sixsamples were produced in each of the experiments, and values measured onthe samples of each experiment were averaged to obtain a more reliableresult. The three-factorial experiments were performed at a dew point ofabout 40 degrees F., water content 12 ppm and included the followingpoints for the three factors:

1. Feed rate was set to indications of 250 and 800 units on the feederdial used. Recall that the feeder rate has a linear dependence on thedial settings, and that a full-scale setting of 999 corresponds to arate of production of about 12 kg per hour (and therefore asubstantially similar material consumption rate). Thus, settings of 250units corresponded to a feed rate of about 3 kg per hour, while settingsof 800 units corresponded to a feed rate of about 9.6 kg per hour. Inaccordance with the standard vernacular used in the theory of design ofexperiments, in the accompanying tables and graphs the former setting isdesignated as a “0” point, and the latter setting is designated as a “1”point.2. The grind air pressure was set alternatively to 85 psi and 110 psi,corresponding, respectively, to “0” and “1” points in the accompanyingtables and graphs.3. The feed air pressure (also known as inject air pressure) was set to60 and 70 psi, corresponding, respectively, to “0” and “1” points.

Turning first to tensile strength measurements, strips of standard widthwere prepared from each sample, and the tensile strength measurement ofeach sample was normalized to a one-mil thickness. The results fortensile strength measurements in length and in width appear in Tables 2and 3 below.

TABLE 2 Tensile Strength in Length FACTORS SAMPLE TENSILE NORMALIZEDFeed Rate, DOE THICKNESS STRENGTH IN TENSILE STRENGTH Exp. No. Grindpsi, Feed psi POINTS (mil) LENGTH (grams) IN LENGTH (g/mil) 1 250/85/600/0/0 6.1 123.00 20.164 2 250/85/70 0/0/1 5.5 146.00 26.545 3 250/110/600/1/0 6.2 166.00 26.774 4 250/110/70 0/1/1 6.1 108.00 17.705 5 800/85/601/0/0 6.0 132.00 22.000 6 800/85/70 1/0/1 5.8 145.00 25.000 7 800/110/601/1/0 6.0 135.00 22.500 8 800/110/70 1/1/1 6.2 141.00 22.742

TABLE 3 Tensile Strength in Width Normalized Factors Tensile Tensile(Feed Rate, Sample Strength Strength Exp. Grind psi, DOE Thickness inLength in Length No. Feed psi) Points (mil) (grams) (g/mil) 1 250/85/600/0/0 6.1 63.00 10.328 2 250/85/70 0/0/1 5.5 66.00 12.000 3 250/110/600/1/0 6.2 77.00 12.419 4 250/110/70 0/1/1 6.1 59.00 9.672 5 800/85/601/0/0 6.0 58.00 9.667 6 800/85/70 1/0/1 5.8 70.00 12.069 7 800/110/601/1/0 6.0 61.00 10.167 8 800/110/70 1/1/1 6.2 63.00 10.161

Table 4 below presents resistivity measurements of a jet milled dryblend of particles provided by dry fibrillization step 20. Note that theresistivity measurements were taken before the mixture was processedinto an electrode film.

TABLE 4 Dry Resistance Factors (Feed Rate, DRY RESISTANCE Exp. No. Grindpsi, Feed psi) DOE Points (Ohms) 1 250/85/60 0/0/0 0.267 2 250/85/700/0/1 0.229 3 250/110/60 0/1/0 0.221 4 250/110/70 0/1/1 0.212 5800/85/60 1/0/0 0.233 6 800/85/70 1/0/1 0.208 7 800/110/60 1/1/0 0.241 8800/110/70 1/1/1 0.256

Referring now to FIGS. 1 i, 1 j, and 1 k, there are illustrated theeffects of the three factors on the tensile strength in length, tensilestrength in width, and dry resistivity. Note that each end-point for aparticular factor line (i.e., the feed rate line, grind pressure line,or inject pressure line) on a graph corresponds to a measured value ofthe quality parameter (i.e., tensile strength or resistivity) averagedover all experiments with the particular key factor held at either “0”or “1,” as the case may be. Thus, the “0” end-point of the feed rateline (the left most point) represents the tensile strength averaged overexperiments numbered 1-4, while the “1” end-point on the same linerepresents the tensile strength averaged over experiments numbered 4-8.As can be seen from FIGS. 1 i and 1 j, increasing the inject pressurehas a moderate to large positive effect on the tensile strength of anelectrode film. At the same time, increasing the inject pressure has thelargest effect on the dry resistance of the powder mixture, swamping theeffects of the feed rate and grind pressure. The dry resistancedecreases with increasing the inject pressure. Thus, all three qualitiesbenefit from increasing the inject pressure.

In Table 5 below we present data for final capacitances measured indouble-layer capacitors utilizing electrode films made from dryfibrillized particles as described herein by each of the 8 experiments,averaged over the sample size of each experiment. Note that C_(up)refers to the capacitances measured when charging double-layercapacitors, while C_(down) values were measured when discharging thecapacitors. As in the case of tensile strength data, the capacitanceswere normalized to the thickness of the electrode film. In this case,however, the thicknesses have changed, because the film has undergonecompression in a high-pressure nip during a process of bonding the filmto a current collector. It is noted in obtaining the particular resultsof Table 5, the electrode film was bonded to a current collector by anintermediate layer of coated adhesive. Normalization was carried out tothe standard thickness of 0.150 millimeters.

TABLE 5 C_(up) and C_(down) Factors Sample (Feed Rate, DOE ThicknessC_(up) Normalized C_(down) NORMALIZED Exp. No. Grind psi, Feed psi)Points (mm) (Farads) C_(up) (Farads) (Farads) C_(down) (Farads) 1250/85/60 0/0/0 0.149 1.09 1.097 1.08 1.087 2 250/85/70 0/0/1 0.133 0.981.105 0.97 1.094 3 250/110/60 0/1/0 0.153 1.12 1.098 1.11 1.088 4250/110/70 0/1/1 0.147 1.08 1.102 1.07 1.092 5 800/85/60 1/0/0 0.1481.07 1.084 1.06 1.074 6 800/85/70 1/0/1 0.135 1.00 1.111 0.99 1.100 7800/110/60 1/1/0 0.150 1.08 1.080 1.07 1.070 8 800/110/70 1/1/1 0.1531.14 1.118 1.14 1.118

In Table 6 we present data for resistances measured in each of the 8experiments, averaged over the sample size of each experiment. Similarlyto the previous table, R_(up) designates resistance values measured whencharging double-layer capacitors, while R_(down) refers to resistancevalues measured when discharging the capacitors.

TABLE 6 R_(up) and R_(down) Factors (Feed Rate, Sample ElectrodeElectrode Exp. Grind psi, DOE Thickness Resistance Resistance No. Feedpsi) Points (mm) R_(up) (Ohms) R_(down) (Ohms) 1 250/85/60 0/0/0 0.1491.73 1.16 2 250/85/70 0/0/1 0.133 1.67 1.04 3 250/110/60 0/1/0 0.1531.63 1.07 4 250/110/70 0/1/1 0.147 1.64 1.07 5 800/85/60 1/0/0 0.1481.68 1.11 6 800/85/70 1/0/1 0.135 1.60 1.03 7 800/110/60 1/1/0 0.1501.80 1.25 8 800/110/70 1/1/1 0.153 1.54 1.05

To help visualize the above data and identify the data trends, wepresent FIGS. 1 m and 1 n, which graphically illustrate the relativeimportance of the three factors on the resulting R_(down) and normalizedC_(up). Note that in FIG. 1 m the Feed Rate and the Grind Pressure linesare substantially coincident. Once again, increasing the inject pressurebenefits both electrode resistance R_(down) (lowering it), and thenormalized capacitance C_(up) (increasing it). Moreover, the effect ofthe inject pressure is greater than the effects of the other twofactors. In fact, the effect of the inject pressure on the normalizedcapacitance overwhelms the effects of the feed rate and the grindpressure factors, at least for the factor ranges investigated.

Additional data has been obtained relating C_(up) and R_(down) tofurther increases in the inject pressure. Here, the feed rate and thegrind pressure were kept constant at 250 units and 110 psi,respectively, while the inject pressure during production was set to 70psi, 85 psi, and 100 psi. Bar graphs in FIG. 1 p illustrate these data.As can be seen from these graphs, the normalized capacitance C_(up) waslittle changed with increasing inject pressure beyond a certain point,while electrode resistance displayed a drop of several percentage pointswhen the inject pressure was increased from 85 psi to 100 psi. Theinventors herein believe that increasing the inject pressure beyond 100psi would further improve electrode performance, particularly bydecreasing internal electrode resistance.

Although dry blending 18 and dry fibrillization step 20 have beendiscussed herein with reference to specific apparatus, it is envisionedthat steps 18 and 20 could be conducted in one step wherein an apparatusreceives dry particles 12, 14, and/or 16 as separate streams to mix theparticles and thereafter fibrillize the particles. Accordingly, it isunderstood that the embodiments herein should not be limited by steps 18and 20, but by the claims that follow. Furthermore, the precedingparagraphs describe in considerable detail inventive methods for dryfibrillizing dry carbon and dry binder mixtures, however, neither thespecific embodiments of the invention as a whole, nor those of itsindividual features should limit the general principles describedherein, which should be limited only by the claims that follow.

In contrast to the additive-based prior art fibrillization steps, thepresent invention provides sufficiently high shear forces without usingprocessing additives, aides, liquids, solvents, or the like.Furthermore, with the present invention no additives are used before,during, or after application of the shear forces. Numerous benefitsderive from non-use of prior art additives including: reduction ofprocess steps and processing apparatus, increase in throughput, theelimination or substantial reduction of residue and impurities that canderive from the use of additives and additive-based process steps, asubstantial reduction or elimination in undesired reactions that canoccur with such residues and impurities, as well as other benefits thatare discussed or that can be understood by those skilled in the art fromthe disclosure provided herein.

The present invention permits that such polymers can be used in thecoating slurry based process described below. In blending step 22 ofFIG. 1 a, an aqueous solution may be added to the compounded dryfibrillized material that was created during dry fibrillization step 20.In one embodiment, the aqueous solution is used to make a slurry, whichcan be used for application of the dry particles 12, 14, and 16 duringan electrode coating process. In one embodiment, the compounded materialprovided by dry fibrillization step 20 is added to 2 to 6 times itsweight of deionized water.

In some cases, after adding an aqueous solution in step 22, clumps orchunks of compounded material may remain in the resulting suspension. Instep 24, if needed, the compounded material can be further mixed tohomogenize the compounded material so as to form a smooth slurry.Alternative aqueous solutions (such as a mixture of water and organicsolvents) and means and methods of homogenizing the compounded particlescan also be used to form the slurry described herein. In step 26, theslurry formed in steps 22 and/or 24 may be applied to a currentcollector. In one embodiment, the slurry is applied to the currentcollector using a doctor blade. Other alternative means and methods forapplying the slurry, such as through a slot die, or a direct or reversegravure process, can also be used in accordance with the presentinvention. In one embodiment, the slurry can be applied to the currentcollector with a thickness of between 50 μm and 600 μm. A lesser orgreater coating thickness is also possible in other embodiments, whichshould be limited only by the claims and their equivalents. In oneembodiment, the current collector comprises an etched or roughenedaluminum sheet, foil, mesh, screen, porous substrate, or the like. Inone embodiment, the current collector comprises a metal, for example,copper, aluminum, silver, gold, and the like. In one embodiment, thecurrent collector comprises a thickness of about 10-50 microns. A lesseror greater collector thickness is also possible in other embodiments,which should be limited only by the claims and their equivalents. Thoseskilled in the art will recognize that if the electrochemical potentialallows, other metals could also be used as a collector.

Prior to applying the slurry to a current collector, an added step 28 oftreating the collector to improve adhesion between the current collectorand the applied slurry can be performed. In one embodiment, the currentcollector can be coated with a bonding agent, layer, or adhesive toimprove the adhesion of the slurry to the collector. For example,carboxymethyl cellulose, melamine, phenolics, or furans can be used as abonding agent between the collector and slurry. In one embodiment,adhesive coating sold under the trade name Electrodag® EB-012 by AchesonColloids Company, 1600 Washington Ave., Port Huron, Mich. 48060,Telephone 1-810-984-5581 is used. Alternatively, other adhesives orbonding agents can be used and/or other methods and means for improvingthe adhesion between the current collector and slurry can be used, suchas treating or physically roughening the surface of the currentcollector prior to application of the slurry.

After the slurry is applied to the collector, it can be dried during adrying step 30 to form an electrode comprising the current collector andcoated slurry of dry fibrillized carbon 12, 14 and binder 16 particles.During the drying step 30, the aqueous solution is evaporated fromwithin the slurry, which results in the formation of a conductiveelectrode film on the current collector. In one embodiment, the slurryis dried in an oven at 85° C. for 1 hour. Alternatively, other methods,times, and temperatures for drying the slurry can be used.

In step 32, the electrodes can be compacted to densify the conductiveelectrode film and further fibrillate the compounded material. In oneembodiment, the film can be compacted using a calender device. Acompacting and/or calendering function can be achieved by a roll-mill,calender, a belt press, a flat plate press, and the like, as well asothers known to those skilled in the art. In one embodiment, thecalender device may comprises a roll-mill. A high-pressure nip at theentry to the roll-mill can be set to gradually decrease the filmthickness by 15% to 60% in 2 to 10 passes.

Referring now to FIG. 2, and preceding Figures as needed, there is seenone possible apparatus for making a coating based electrode according tothe present invention. In one embodiment seen in FIG. 2, a slurry orsuspension made from dry fibrillized dry carbon and dry binder particles12, 14, and 16 can be held in a suspension feeder 34, and a currentcollector 36 in the form a roll of aluminum foil, coated if needed withan adhesive/bonding agent, can be held on a feeding roll 38. Thecollector 36 may be wrapped around a roller 39, positioned beneath acoating head 40 and adjacent to the suspension feeder 34. As thecollector 36 moves across the roller 39, a suspension of slurry is fedfrom the coating head 40 onto a surface of the collector 36. From there,the collector 36 is carried through an oven 42, which is configured forremoving any of the solution(s) used. The dried slurry forms aconductive electrode film on the collector 36. Next, the collector maybe fed through a series of rollers 44 configured to compact and calenderthe dried slurry and current collector so that densification and furtherfibrillization occurs. After calendaring, a finished electrode 46 isgathered on a storage roll 48 where it may be stored until it isassembled into a finished energy storage device.

Referring now to FIG. 3, and preceding Figures as needed, duringmanufacture, one or more finished electrode 1200 coated with one or moreslurry made accordance with embodiments disclosed herein is rolled intoa configuration known to those in the electrode forming arts as ajellyroll. Not shown is a separator disposed within the jellyroll, whichacts to separate layers of the rolled electrode 1200. The rolledelectrode 1200 is inserted into an open end of a housing 2000. Aninsulator (not shown) is placed along a top periphery of the housing2000 at the open end, and a cover 2002 is placed on the insulator.During manufacture, the housing 2000, insulator, and cover 2002 may bemechanically curled together to form a tight fit around the periphery ofthe now sealed end of the housing, which after the curling process iselectrically insulated from the cover by the insulator. When disposed inthe housing 2000, the electrode may be configured such that respectiveexposed collector extensions 1202 of the electrode make internal contactwith the bottom end of the housing 2000 and the cover 2002. In oneembodiment, external surfaces of the housing 2000 or cover 2002 mayinclude or be coupled to standardized connections/connectors/terminalsto facilitate electrical connection to the rolled electrode 1200 withinthe housing 2000. Contact between respective collector extensions 1202and the internal surfaces of the housing 2000 and the cover 2002 may beenhanced by welding, soldering, brazing, conductive adhesive, or thelike. In one embodiment, a welding process may be applied to the housingand cover by an externally applied laser welding process. In oneembodiment, the housing 2000, cover 2002, and collector extensions 1202comprise substantially the same metal, for example, aluminum. Anelectrolyte can be added through a filling/sealing port (not shown) tothe sealed housing 1200. In one embodiment, the electrolyte is 1.5 Mtetrametylammonium or tetrafluroborate in acetonitrile solvent. Afterimpregnation and sealing, a finished product is thus made ready forcommercial sale and subsequent use.

Although the particular systems and methods herein shown and describedin detail are fully capable of attaining the above described objects ofthe invention, it is understood that the description and drawingspresented herein represent some, but not all, embodiments that arebroadly contemplated. Structures and methods that are disclosed may thuscomprise configurations, variations, and dimensions other than thosedisclosed. For example, capacitors as a broad class of energy storagedevices are within the scope of the present invention, as are, withappropriate technology based modifications, batteries and fuel cells.Also, different housings may comprise coin-cell type, clamshell type,prismatic, cylindrical type geometries, as well as others as are knownto those skilled in the art. For a particular type of housing, it isunderstood that appropriate changes to electrode geometry may berequired, but that such changes would be within the scope of thoseskilled in the art.

Thus, the scope of the present invention fully encompasses otherembodiments that may become obvious to those skilled in the art and thatthe scope of the present invention is accordingly limited by nothingother than the appended claims and their equivalents.

1. A blend of dry particles fibrillized for use in the manufacture of acoated electrode, comprising: a mixture of dry fibrillized dry carbonand dry binder particles.
 2. The particles of claim 1, wherein the drybinder particles comprise a polymer, and wherein the dry carbonparticles comprise activated and conductive carbon.
 3. The particles ofclaim 2, wherein the binder comprises particles subjected to high shearforces.
 4. The particles of claim 3, wherein the high shear forces areapplied by gas at more than about 60 PSI.
 5. The particles of claim 3,wherein the binder comprises milled polymer particles.
 6. The particlesof claim 3, wherein the binder comprises jet milled polymer particles.7. The particles of claim 3, wherein the binder comprises hammer milledpolymer particles.
 8. The particles of claim 2, wherein the bindercomprises fluoropolymer particles.
 9. The particles of claim 8, whereinthe binder comprises PTFE.
 10. The particles of claim 8, wherein theelectrode is an energy storage device electrode.
 11. The particles ofclaim 10, wherein the energy storage device is a capacitor.
 12. Anelectrode, comprising; a dry blend of dry carbon particles and drybinder particles subjected to high shear forces.
 13. The electrode ofclaim 12, wherein the blend comprises approximately 50% to 99% activatedcarbon.
 14. The electrode of claim 12, wherein the blend comprisesapproximately 0% to 25% conductive carbon.
 15. The electrode of claim12, wherein the blend comprises approximately 0.5% to 20% fluoropolymer.16. The electrode of claim 12, wherein the blend comprises approximately80% to 95% activated carbon, approximately 0% to 15% conductive carbon,and approximately 3% to 15% fluoropolymer.
 17. The electrode of claim12, wherein the electrode is a capacitor electrode.
 18. The electrode ofclaim 17, wherein the electrode is a double-layer capacitor electrode.19. The electrode of claim 12, wherein the electrode is a batteryelectrode.
 20. The electrode of claim 12, wherein the electrode is afuel-cell electrode.
 21. The electrode of claim 12, further comprising acurrent collector, wherein the binder and carbon particles are in theform of a coated dried slurry, wherein the slurry is coupled to thecurrent collector.
 22. A capacitor product, comprising; a dryfibrillized blend of dry particles subjected to high shear forces, theparticles including binder and carbon particles; and one or more currentcollector, wherein the blend of dry particles are disposed onto the oneor more current collector as a coating.
 23. The product of claim 22,wherein between the one or more current collector and the dry particlesis disposed a bonding layer.
 24. The product of claim 22, wherein theone or more current collector comprises aluminum.
 25. The product ofclaim 24, further comprising a housing, wherein the one or more currentcollector is shaped as a roll, wherein the roll is disposed within thehousing.
 26. The product of claim 25, wherein within the housing isdisposed an electrolyte.
 27. The product of claim 26, wherein theelectrolyte comprises acetonitrile.
 28. The product of claim 22, whereinthe capacitor is rated to operate at a voltage of no more than about 3.0volts.
 29. An energy storage device, comprising: dry fibrillizedelectrode means for providing coated electrode functionality in anenergy storage device.
 30. A capacitor, the capacitor comprising: ahousing; a cover; a collector, the collector disposed in the housing,the collector comprising two ends, a first end coupled to the housing, asecond end coupled to the cover; a dried electrode slurry, the driedelectrode slurry disposed as a coating onto the collector, the driedelectrode slurry comprising a dry fibrillized blend of dry carbon anddry polymer, the dry fibrillized blend comprising of essentially noprocessing additive; and an electrolyte, the electrolyte disposed in thehousing.
 31. The capacitor of claim 30, wherein the capacitor comprisesa capacitance of greater than 1 Farad.